Power allocation in OFDM cognitive radio relay networks with average interference constraints

In this paper, we study power allocation in OFDM based cognitive radio (CR) relay networks when the fading statistics between cognitive and primary users are known at the CR transmitters. The objective of power allocation is to maximize the instantaneous capacity of the CR network. Optimal power allocation schemes are developed for both decode-and-forward (DF) and amplify-and-forward (AF) relay assisted CR transmission where the primary users are subject to average interference constraints and the CR transmitters are subject to maximum transmit power constraint. Performance of the proposed schemes is compared with uniform power allocation method and the numerical results confirm that the proposed optimal power allocation schemes achieve significant capacity improvement compared to uniform power loading.